The present invention relates to wireless communication systems, such as a wireless local area network (WLAN).
WLANs based on the IEEE 802.11b standard, IEEE std. 802.11b-1999 (published Sep. 16, 1999) (also known as “WiFi”) are beginning to proliferate homes and businesses to provide data communications to roaming devices, such as notebook computers, personal digital assistants, advanced cellular telephones, and the like. Although the IEEE standard promises 11 megabit per second (Mbps) performance with a reach of hundreds of feet, in typical use, due to the presence of noise and multipath inter-symbol interference (ISI), performance fails to achieve this objective.
Wireless channels suffer from two main impairments, multipath induced ISI and additive noise. Multipath induced ISI occurs when energy from a transmitter to a receiver arrives via multiple paths. When the difference in propagation time among the paths is large relative to a symbol period, any sample in time can contain energy from multiple transmitted signals.
Two types of ISI exist in block-coded communications: “inter-codeword interference” and “intra-codeword interference.” Inter-codeword interference is energy from symbols in one codeword that spreads into the symbols of another codeword, while intra-codeword interference is energy from symbols in one codeword that spreads into symbols within that same codeword.
While different measures may be used to detect in the presence of noise and ISI, such as a rake receiver, a decision feedback equalizer (DFE), or a DFE with an embedded or cascaded block detector, drawbacks exist. Some measures do not resolve both additive noise and ISI, while others do not resolve both intra-codeword and inter-codeword interference. Still others are not computationally efficient. Thus a need exists to improve robustness of detection in the presence of noise and ISI in a computationally efficient manner.